1. Field of the Invention
The present invention relates to an organic electroluminescence unit which serves as pixels in an active matrix display panel.
2. Description of the Related Art
At present, an electroluminescence element (hereinafter referred to as xe2x80x9cEL elementxe2x80x9d) using an organic material and the like for a light emitting layer, for example, is known as a light emitting element for use in a display panel. The EL element can be equivalently represented by a capacitive component, and a component of diode characteristic connected in parallel with the capacitive component. As a DC voltage is applied between electrodes of the EL element, a charge is accumulated on the capacitive component, and a drive current begins to flow as the accumulated charge exceeds a light emission threshold voltage. This causes the EL element to emit light at an intensity proportional to the drive current.
The EL elements include a red light emitting EL element having a structure for emitting light in red; a green light emitting EL element having a structure for emitting light in green; and a blue light emitting EL element having a structure for emitting light in blue. Thus, these three types of EL elements, emitting light in red, blue and green, form a single EL display unit serving as a pixel, and a number of EL display units are arranged in matrix on a panel which defines one screen, to thereby constitute a color display panel.
However, the red light emitting EL element, green light emitting EL element, and blue light emitting EL element are different from one another in the intensity of light emitted therefrom with respect to a constant (or same) drive current. Therefore, in order to provide an appropriately displayed image corresponding to an input video signal, level adjustments must be made, for example, for each of red, green and blue components at the stage of this input video signal, or different voltages must be applied to the EL elements for respective colors of emitted light, thus giving rise to a problem of a complicated configuration.
An object of the present invention is to provide an EL display unit which is capable: of realizing an appropriate image display corresponding to an input video signal in a simple configuration.
According to one aspect of the present invention, there is provided an electroluminescence display unit including a plurality of electroluminescence elements for emitting light in different colors respectively, and a plurality of driving transistors associated with the electroluminescence elements respectively for generating drive currents to cause the electroluminescence elements to emit light respectively, wherein the driving transistors have channel widths decided to generate the drive currents in a certain ratio, with which currents the electroluminescence elements emit light at desired intensities respectively.
When three colors of light, namely red, green and blue, are concerned, each of the electroluminescence elements serving to emit red, green or blue light can be driven to emit light at a desired intensity, using a single power supply voltage. It is therefore possible to achieve an appropriate image display corresponding to an input video signal in a display device having a simple structure. Such electroluminescence display unit needs neither a circuit for adjusting the level of the input video signal for each color component, nor a power supply circuit for generating different power supply voltages for the respective colors.
The driving transistors may have channel lengths, instead of the channel widths, to generate the drive currents in the predetermined ratio, with which currents the electroluminescence elements emit light at the desired intensities respectively.